Fibrous material having densified surface for improved air flow resistance and method of making

ABSTRACT

The present invention provides a fibrous veil having a plurality of densified portions formed thereon for improved airflow resistance. The airflow resistance may be tuned to meet the needs of a particular application by selecting the size, density and location of the densified portions. The veil may be used independently or in combination with other sound control materials. The present invention also provides a fibrous blanket having a plurality of densified portions formed on one or both major surfaces thereof for improved airflow resistance. The airflow resistance may be tuned to meet the needs of a particular application by selecting the size and density of the densified portions. A method of manufacturing the materials of the present invention by applying heat and/or pressure to portions of the material is also presented.

TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION

The present invention relates generally to acoustical products, and more particularly, to fibrous blanket materials having a plurality of densified portions formed on a surface thereof for improved airflow resistance. The airflow resistance may be tuned to meet the needs of a particular application by selecting the size and density of the densified portions.

BACKGROUND OF THE INVENTION

Sound insulation materials are used in a variety of settings where it is desired to dampen noise from an external source. For example, insulation materials have been used in applications such as in appliances to reduce the sound emitted into the surrounding areas of a home, in automobiles to reduce mechanical sounds of the motor and road noise, and in office buildings to attenuate sound generated from the workplace. Acoustical insulation typically relies upon both sound absorption (that is, the ability to absorb incident sound waves) and transmission loss (that is, the ability to reflect incident sound waves) in order to provide sound attenuation. Conventional acoustical insulation materials include materials such as foams, compressed fibers, fiberglass batts, felts, and nonwoven webs of fibers such as meltblown fibers. Laminates of one or more layers of fibrous insulation and one or more layers of a dense fibrous veil are known to provide sound absorption and transmission loss. Examples of conventional acoustical insulation materials and laminates are set forth below.

U.S. Pat. No. 4,766,029 to Brock et al. discloses a semi-permeable non-woven laminate formed of polypropylene and polyethylene sandwiched between two spunbond layers of polypropylene.

U.S. Pat. No. 5,886,306 to Patel et al. discloses a layered acoustical insulating web that includes a series of cellulose fiber layers sandwiched between a layer of melt-blown or spun-bond thermoplastic fibers (such as polypropylene) and a layer of film, foil, paper, or spunbond thermoplastic fibers.

U.S. Pat. No. 6,358,592 to Vair, Jr., et al. discloses a melt-blown fibrous insulation that includes a fibrous layer of randomly oriented, air laid, thermoplastic fibers and two thin integral skins. The skins include fine holes or openings that exhibit significant airflow resistivity that not only reflect sound waves but also function as an airflow resistance barrier that enhances sound absorption properties.

U.S. Pat. No. 6,669,265 to Tilton et al. describes a fibrous material that has a lofty, acoustically insulating portion and a relatively higher density skin that may function as a water barrier. The fibrous material includes polyester, polyethylene, polypropylene, polyethylene terephthalate, glass fibers, natural fibers, and mixtures thereof.

U.S. Patent Application Publication No. 2003/0039793 to Tilton et al., herein incorporated by reference, describes a trim panel insulator for a vehicle that includes a nonlaminate acoustical and thermal insulating layer of polymer fibers. The insulator may also include a relatively high density, nonlaminate skin formed by localized heating of the surface of the insulating layer and/or one or more facing layers formed of polyester, polypropylene, polyethylene, rayon, ethylene vinyl acetate, polyvinyl chloride, fibrous scrim, metallic foil, and mixtures thereof.

U.S. Patent Application Publication No. 2004/0002274 to Tilton, herein incorporated by reference, discloses a laminate material that includes a base layer formed of polyester, polypropylene, polyethylene, fiberglass, natural fibers, nylon, rayon, and blends thereof and a facing layer. The base layer has a density of from approximately 0.5-15.0 pcf and the facing layer has a density of between about 10 pcf and about 100 pcf.

U.S. Patent Application Publication No. 2004/0077247 to Schmidt et al. describes a nonwoven laminate that contains a first layer that contains thermoplastic spunbond filaments having an average denier less than about 1.8 dpf (2.0 dtex) and a second layer containing thermoplastic multicomponent spunbond filaments having an average denier greater than about 2.3 dpf (2.55 dtex). The laminate has a structure such that the density of the first layer is greater than the density of the second layer and the thickness of the second layer is greater than the thickness of the first layer.

The methods of controlling the formation of a densified blanket set forth in the prior art require that predetermined thicknesses be maintained within very close tolerances. Typical fibrous blankets of the prior art are formed having tolerances of ±0.010 inches (±0.25 mm). Meeting such stringent tolerances is difficult when a blanket of randomly distributed fibers is heated to a controlled temperature, pressure and time to control the density and airflow resistance required to “tune” a fibrous blanket to attenuate noise at selected frequencies.

Although there are numerous acoustical insulation products in the art, there exists a continuing need for acoustical insulation materials that exhibit superior sound attenuating properties, that can be tuned relatively easily to control a desired frequency, and that are lightweight and low in both material cost and processing cost.

SUMMARY OF THE INVENTION

The present invention provides a fibrous veil having a plurality of densified portions formed thereon for improved airflow resistance, and provides a fibrous material having improved airflow resistance that may be tuned to meet the needs of a particular application by selecting the size and density of the densified portions. The veil may be used independently or may be used in combination with other sound control materials.

The present invention also provides a fibrous blanket that contains a plurality of densified portions formed on one or both major surfaces thereof for improved airflow resistance. The airflow resistance may be tuned to meet the needs of a particular application by selecting the size and density of the densified portions on the fibrous blanket.

A method of manufacturing the materials of the present invention by applying heat and/or pressure to portions of the material by localized densification of the surface is also presented.

The features and advantages of the invention will appear more fully hereinafter from a consideration of the Detailed Description that follows. It is to be expressly understood, however, that the drawings are for illustrative purposes and are not to be construed as defining the limits of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages of this invention will be apparent upon consideration of the following Detailed Description of the Invention, especially when taken in consideration of the accompanying Drawings.

FIG. 1 is a schematic illustration of a foraminous roller used to provide densified portions on the surface of a fibrous blanket according to at least one exemplary embodiment of the present invention;

FIG. 2 is a cross sectional view of the roller and blanket of FIG. 1 showing the compression of the fibrous blanket by the roller to provide densified surfaces according to at least one exemplary embodiment of the present invention;

FIG. 3A is a cross sectional view of a roller and blanket showing the compression of the fibrous blanket by the roller to provide an alternate patterned densified surfaces according to at least one exemplary embodiment of the present invention; and

FIG. 3B is a cross sectional view of a roller and a lofty fibrous blanket showing compression of one surface of a lofty fibrous blanket by the roller to provide an alternate patterned densified surfaces according to at least one exemplary embodiment of the present invention;

FIG. 4 is a graph illustrating the relationship between percentage of compressed area and acoustical impedance (Airflow) in Rayls; and

FIG. 5 is a graph illustrating the relationship between the Log of the percentage of compressed area and the Log of the acoustical impedance (Airflow).

DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS OF THE INVENTION

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are described herein. All references cited herein, including published or corresponding U.S. or foreign patent applications, issued U.S. or foreign patents, or any other references, are each incorporated by reference in their entireties, including all data, tables, figures, and text presented in the cited references.

In the drawings, the thickness of the lines, layer, and regions may be exaggerated for clarity. It will be understood that when an element such as a layer, region, or substrate is referred to as being “on” another element, it can be directly on the other element or intervening elements may also be present. It will also be understood that when an element such as a layer, region, or substrate is referred to as being “over” another element, it can be directly over the other element, or intervening elements may be present. The terms “top”, “bottom”, “side” and the like are used herein for the purpose of explanation only. It is to be noted that like numbers found throughout the figures denote like elements.

The invention relates to an acoustical product that includes at least one fibrous web having densified portions. The partially densified fibrous web may be utilized in a number of applications such as in appliances, in office screens and partitions, in ceiling tiles, in building panels, and in automobiles (for example, headliners, dash insulators, hood liners, floor liner, trim panels, and the like).

The sound attenuation provided by the present invention may be used in a variety of environments in which the sounds requiring attenuation may differ in both amplitude and frequency. Advantageously, according to one aspect of the present invention, the acoustical properties or characteristics of the fibrous insulation blanket may be tuned to provide the best possible sound attenuating performance for the particular product application by varying the size, shape, and spacing of the densified portions.

A fibrous web 10 may be formed into a patterned web 12 having a plurality of undensified portions 14 and densified portions 16 is illustrated in FIG. 1. The fibrous web may be formed of an air-laid, wet-laid, spunbonded or meltblown non-woven mat of randomly oriented thermoplastic fibers or alternatively may be formed by a combination of theses methods, for example spunbond-meltblown or spunbond-meltblown-spunbond, or of a woven or patterned mat of thermoplastic fibers. Other conventional methods for forming a mat of thermoplastic fibers may also be used. Preferably, the fibrous web 10 is formed by a wet-laid process. For example, a wet-laid mat of thermoplastic fibers may be made by melting a polymeric material within a melter or die and extruding the molten polymeric material through a plurality of orifices to form continuous filaments. As the polymer filaments exit the orifices, they are introduced directly into a high velocity air stream that attenuates the filaments and forms discrete, individual polymeric fibers. The polymeric fibers are then cooled and cut to a predetermined length. The fibers are then processed using a conventional wet laid process to form a non-woven fibrous mat.

The fibrous web 10 includes polymer based thermoplastic materials such as, but not limited to, polyester, polyethylene, polypropylene, polyethylene terephthalate (PET), polyphenylene sulfide (PPS), polyvinyl chloride (PVC), polyolefins, polyamides, polysulfides, polycarbonates, rayon, and other suitably fiberizable thermoplastic materials and mixtures thereof. In addition, the fibrous web 10 may include glass fibers, natural fibers (such as hemp, kenaf, and cotton), and combinations thereof. The term “natural fiber” as used in conjunction with the present invention is intended to refer to plant fibers extracted from any part of a plant, including, but not limited to, the stem, seeds, leaves, roots or bast. The fibrous web may also include a portion of moldable materials such as latex, epoxy power, or thermoplastic flakes, particles or powder.

In at least one embodiment, the fibrous web 10 includes heat fusible fibers such as multicomponent fibers. Multicomponent fibers may be formed of two or more polymers combined to form fibers having a core of one polymer and a surrounding sheath of the other polymer, two polymers combined in a side-by-side relationship, an islands-in-the-sea configuration or any other configuration. When multicomponent fibers are used as a component of the fibrous web 10, the multicomponent fibers may be present in any percentage of the total fibers.

The fibrous web 10 may be formed into a patterned web 12 having undensified portions 14 and densified portions 16 by applying heat and/or pressure to a major surface (such as the top side) of the fibrous web 10. One method of forming the patterned web 12 is shown in FIG. 1. As shown, the fibrous web 10 is passed under a roller assembly 20, which includes a roller 22, which compress the fibrous web 10 to form densified portions 14, and apertures 24, which form undensified portions 16. The roller 22 is rotatably mounted on an axel 26.

FIG. 2 shows a cross section, taken along line 2-2 of FIG. 1, showing the interaction of roller 20 and fibrous web 10. As can be seen in FIG. 2, the apertures 24 correspond to the undensified portions 16 and the roller 22 compresses fibrous web 10 to form densified portions 14. While it is apparent from FIG. 1 that there may be a single densified portion 16 surrounding the undensified portions 14, it is possible to form the densified and undensified portions in any design including interconnected or disconnected undensified portions 14 and interconnected or disconnected densified portions 16.

An alternate version of roller assembly 20 is shown in FIG. 3A and FIG. 3B in which the roller 22 includes protrusions 30 rather than apertures 24. Although a roller assembly 20 is shown it is contemplated it would be apparent to one in the art, based on the teachings hereof, to use any number of forming techniques. For example, the fibrous web 10 may be patterned by any suitable method including pressing a cold web with a heated roller or stamp, or alternatively heating the web by, for example, infrared heating, forced hot air, microwave emission, ultrasonic energy, and then pressing with a cold roller or stamp. It is also possible to press the web when it is formed to take advantage of the heating of the web to bond the fibers in the web fabrication process. In the embodiment of the present invention shown in FIG. 1 the roller 22 is heated to a temperature above the softening point of the fibers of fibrous web 10. In the case of multicomponent fibers, the temperature of roller 22 is raised to a temperature sufficient to soften the low melting point thermoplastic but not the high melting point thermoplastic of the multicomponent fibers. The softened low melting point thermoplastic acts as a binder between adjacent fibers and causes the fibers to bond together in a densified form.

As shown in FIG. 3A, the fibrous web 10 is passed under roller 22 where the fibrous web 10 is compressed by protrusions 30 to form densified portions 16 in the area of the protrusions 30 and is uncompressed to form undensified portions 14 in the area of the roller 22. The patterned web 12 is then cooled to set the patterned web 12 in the form depicted in FIG. 3A. Cooling platens, cooling fans, or any other appropriate structure or combination of structures capable of rapidly cooling the first fibrous insulation blanket 10 may be utilized to cool the patterned web 12.

As shown in FIG. 3B, a top portion of a lofted fibrous blanket 40 may be densified as the blanket 40 passes under a roller 22 heated to a temperature above the softening point of the fibers of blanket 40 to densify portions and form a patterned lofted fiberized product. The protrusions 30 compress the blanket 40 to form densified portions 16 in the surface of patterned blanket 42. It is also possible to use opposed patterned roller assemblies 20 to form complex patterned surfaces. It is also possible to form a patterned blanket 42 having a quilted surface where the blanket 40 includes fully densified portions 16 similar to that shown n FIG. 3A but with a lofty blanket 40 forming the uncompressed areas. Additional patterned webs 12 may be used as a facing layer on one or both major surfaces of the patterned lofty blanket to form and acoustical insulation product. Additional facing layers formed of polyester, rayon, metallic foil, or an additional patterned web 12 may be applied to the major surface opposite the patterned web.

According to one aspect of the present invention, as described above patterned web 12 may be formed on the fibrous insulation material 10 to create a specific airflow resistance and/or to achieve a desired acoustic performance. For example, multiple patterned webs 12 according to the present invention may be used in an acoustic insulation product. Typically, airflow resistances greater than 300 Rayls are desired and 500-3500 Rayls are preferred. A single patterned web 12 may be tuned by altering the size shape and density of the densified portions to yield a product that has a predetermined airflow resistance and acoustic performance. Laminates of multiple layers of patterned webs 12, fibrous blankets as well as other materials such as polyester, rayon, metallic foil may be added to the laminate.

Having generally described this invention, a further understanding can be obtained by reference to certain specific examples illustrated below which are provided for purposes of illustration only and are not intended to be all inclusive or limiting unless otherwise specified.

EXAMPLES

Acoustical veils were fabricated according to the present invention by pressing a patterned foraminous plate heated to 375° F. between top and bottom plates on a 30-ton press. The wet process veil used is a 100 gram per square meter, 1.5 denier PET and 1.5-denier PET/PET bicomponent fiber blend. The temperature and pressure cause the veil to densify to between 75% to 100% of the density of the material of the unprocessed veil. The resulting acoustical veils had densified areas of about 40%, 58% and 90% and were determined to have acoustical impedances of 500, 1300 and 3500 Rayls. The pattern and properties of the veils are shown in Table 1. The Log of the acoustical impedance (Rayls) and the Log of the percentage of compressed area are shown in Table 2. TABLE 1 Ex. 1 Ex. 2 Ex. 3 Individual Circle Area (mm) 31.67 7.92 1.94 Undensified Area (mm²) 2216.84 1615.13 185.85 Total Area (mm²) 3658.27 3844.55 1800.87 Densified Area (mm²) 1441.43 2229.42 1615.02 % Compressed 39.40 57.99 89.68 % Raised 60.60 42.01 10.32 Ratio C/R (—) 0.65 1.38 8.69 Acoustical Impedance (Rayls) 500 1300 3500 Ratio C/R (—) 0.65 1.38 8.69

TABLE 2 Rayls Log Rayls % Comp. Log Comp. 500 2.698 39.40 1.595 1300 3.113 57.99 1.763 3500 3.544 89.68 1.952

From this data the Formula 1 may be derived: Log (Rayls)=−1.07+2.36 Log (% Densified Area)  (1)

While it is to be expected that this formula is dependent upon material, shape of densified areas and undensified areas, Formula 1 demonstrates that the acoustical impedance can be predetermined and that a tuned acoustical web may be fabricated.

The invention of this application has been described above both generically and with regard to specific embodiments. Although the invention has been set forth in what is believed to be the preferred embodiments, a wide variety of alternatives known to those of skill in the art can be selected within the generic disclosure. The invention is not otherwise limited, except for the recitation of the claims set forth below. 

1. A patterned acoustical web, comprising: a fibrous web having a plurality of areas of a first density formed thereon and at least one area of a second density formed thereon, wherein the combination of the first density and the second density form a web having a predetermined acoustical impedance.
 2. The patterned acoustical web of claim 1, wherein said first density is greater than said second density.
 3. The patterned acoustical web of claim 1, wherein said second density is approximately equal to a density of the fibrous web prior to densification.
 4. The patterned acoustical web of claim 1, wherein the fibrous web is formed of a material having a material density and said first density is equal to at least 75% of the material density.
 5. The patterned acoustical web of claim 1, wherein said first density is greater than said second density.
 6. The patterned acoustical web of claim 1, wherein said acoustical impedance has a value between about 300 and 3500 Rayls.
 7. The patterned acoustical web of claim 6, wherein said acoustical impedance has a value between about 1300 and 3500 Rayls.
 8. The patterned acoustical web of claim 1, wherein said second density is greater than said first density.
 9. The patterned acoustical web of claim 1, wherein the area the first density is between about 40 and 90 percent of the surface area of the fibrous web.
 10. The patterned acoustical web of claim 1, wherein said densified area extends from a first major surface of the fibrous web to a second major surface of the fibrous web.
 11. A lofted fibrous acoustical insulation product, comprising: a lofted fibrous acoustical material having formed on the surface thereof, a plurality of areas of a first density; and at least one area of a second density, wherein acoustical material has an acoustical impedance greater than about 300 Rayls.
 12. The fibrous acoustical insulation product of claim 11, wherein said first density is greater than said second density.
 13. The fibrous acoustical insulation product of claim 11, wherein said first density is greater than said second density.
 14. The fibrous acoustical insulation product of claim 11, further comprising at least on additional layer of an acoustical material.
 15. The fibrous acoustical insulation product of claim 14, wherein said acoustical impedance has a value of about 500 to 3500 Rayls.
 16. The fibrous acoustical insulation product of claim 11, wherein area of a first density is between about 40 and 90 percent of the surface area of the fibrous web.
 17. A method of manufacturing an acoustical product comprising the steps of: providing a fibrous material; densifying at least 40% of the surface of said fibrous material; and forming a patterned densified surface, to provide an acoustical product having acoustical impedance has a value greater than about 300 Rayls.
 18. The method of claim 17, wherein said acoustical impedance has a value between about 300 and 3500 Rayls.
 19. The method of claim 18, wherein said acoustical impedance is between 1300 and 3500 Rayls.
 20. The method of claim 17, wherein said acoustical product includes a substantially undensified bulk material underlying said patterned densified surface. 